Electroluminescent lamp devices and their manufacture

ABSTRACT

An electroluminescent lamp unit includes a flat deformable substrate of preselected size having smaller sheet-form flexible electroluminescent lamps secured face-to-face at preselected positions on a surface of the substrate, the lamps connected with conductive traces on the substrate. The flat substrate with secured lamps can be deformed into a desired shape to provide a relatively inexpensive and reliable electroluminescent lamp unit applicable for a wide variety of applications. The flexible electroluminescent lamps of the unit can be individually addressable and may have different colors or intensities. A method of manufacture of such units employs surface mount technology in an automated version, pick and place robots select and place the lamps as instructed, followed by ultrasonic welding or mechanical or adhesive fastening.

This is a continuation of application Ser. No. 08/407,269, filed Mar.20, 1995, now U.S. Pat. No. 5,565,733; which is a continuation ofapplication Ser. No. 07/991,295, filed Dec. 16, 1992, which isabandoned.

BACKGROUND OF THE INVENTION

This invention relates to the achievement of low cost and versatileelectroluminescent lamp products.

As is known by those in the art, an electroluminescent lamp is asurface-area light source consisting of a suitable phosphor placedbetween electrodes, one of which is essentially transparent. When analternating current is applied between the electrodes the phosphor emitslight, the color of the light dependent on the choice of phosphor.

Such lamps are suitable for a wide variety of applications, includingilluminated instrument panels, dial indicators, signs and the like. Suchelectroluminescent lamp panels can be fabricated by applying a generalcoating of conductive material, such as indium tin oxide, over theentire substrate panel, the coating providing the material for one ofthe electrodes, upon which the phosphor and rear electrode layers areapplied. In many applications, the full surface of the panel is notrequired to be light emitting and the unlit portion is masked byprinting an opaque ink on the front surface of the lamp. Alternatively,as described in U.S. Pat. No. 4,904,901, material (indium tin oxide)corresponding to the transparent layer is deposited over an entiresurface of the panel and is thereafter removed from most of the surfacewith an acid etch leaving behind areas corresponding to discrete areasof illumination. The phosphor and rear electrode layers are thendeposited over the discrete areas. Likewise, either the phosphor or therear electrode can be applied over desired areas using techniqueswell-known in the art.

SUMMARY OF THE INVENTION

According to the invention, for forming a modular lamp unit, flat-formflexible electroluminescent lamps of selected limited size are placedand secured upon a larger printed circuit substrate employing surfacemount techniques. The substrate and secured lamps can be subsequentlydeformed into a desired shape or incorporated as is into a product.Alternatively, the lamp and the substrate may be subject to separatepreforming operations and can then be joined together. In all thesecases, the area occupied by the lamp is restricted solely to the areadesired to be illuminated. Thus, the invention reduces production costby significantly reducing the area covered by the lamp. As is known inthe art, conductive materials (e.g. indium tin oxide) used to provide anelectrode of the lamp can be relatively expensive. Further, smallersegmented and individually addressable lamps consume less electricalpower, generate less heat and are more reliable than large full arealamps having opaque patterns over unlit portions of the lamp. Opaquepatterns for covering lit line traces between desired areas ofillumination are also eliminated. Automation of the process for placingand securing individual lamps is preferably achieved by programmed pickand place robots for selecting and placing the lamp on the surface of areceiving printed circuit substrate according to pre-specifiedinstructions, followed by automated steps to connect and secure thelamps to the substrate.

Shaping the lamps and substrate permits their use in a wide variety ofapplications, e.g., to accommodate special aesthetic designs or wherespace is limited. In addition, the flexible nature of the lamps and useof a flexible substrate permit their use in applications where theflexible substrate is actuated, such as in the opening and closing of acassette player door. Novel thermalforming techniques enable molding ofa preformed lamp member into a stable desired three-dimension shapewithout impairing the function of the lamp.

The invention also permits a number of lamps to be provided onto aprinted circuit substrate, each lamp or separate groups beingindependently addressable and having different colors or brightnesscharacteristics. Individually addressable lamps of the unit may beindividually driven or may be powered by a single power supply.

In one aspect, the invention includes providing a supporting substrateof preselected size having conductive traces for energizingelectroluminescent lamps. A plurality of electroluminescent lamps, eachlamp smaller than the supporting substrate, are placed and secured inflat form face-to-face (flat surface to flat surface) at preselectedpositions upon the supporting substrate and are electrically connectedto the conductive traces of the supporting substrate. (The face-to-faceengagement may involve either the front face or the back face of theelectroluminescent components, depending upon the particularconstruction employed).

In another aspect, the invention provides an electroluminescent lampunit by the following steps. A deformable supporting substrate ofpreselected size and having a first flat configuration and conductivetraces for energizing an electroluminescent lamp is provided. At leastone sheet-form flexible electroluminescent lamp is placed face-to-facein a preselected position upon and secured to the supporting substrateand is electrically connected to the conductive traces. The supportingsubstrate and secured sheet-form lamp are then deformed into a desiredconfiguration for use.

In another aspect of the invention, the supporting substrate is flexibleand after securing at least one sheet-form electroluminescent lamp tothe substrate the supporting substrate and secured lamp are deformedinto a desired configuration.

In another aspect, a method of constructing a three dimensionalilluminating object comprising, forming a lamp member by providing upona generally sheet-form, light-transmitting thermoplastic carriersubstrate an electroluminescent lamp comprised of a thin filmtransparent electrode deposited on the carrier substrate and, thereon, aplurality of intimately bonded superposed thermoplastic layers includinga layer containing phosphor particles that forms a phosphor layer, aninsulative layer and a back conductive electrode layer, placing the lampmember over a die of desired three dimensional shape, and pressureforming the lamp member by pressing the lamp member against the die toform the lamp member to the desired three dimensional shape underconditions maintaining the operational integrity of the carriersubstrate and the thermoplastic layers to produce a formed shape capableof emitting light.

Embodiments of the invention include the following aspects. The step ofelectrically connecting the lamp to the conductive traces and securingthe lamp to the supporting substrate is accomplished by a single step.The lamp has exposed conductive leads which are ultrasonically welded tothe conductive traces of the supporting substrate. The sheet-form lampis electrically connected to the supporting substrate with a mechanicaldevice (e.g. mechanical eyelet) placed through the combined thickness ofthe lamp and substrate. The sheet-form electroluminescent lamp includesa strain relief and the desired final configuration of the deformedsubstrate and secured lamp is a complex shape.

Where multiple lamps are employed, a first one of the electroluminescentlamps has a light emitting characteristic (e.g. color, intensity) thatis different than a light emitting characteristic of a second one of theelectroluminescent lamps.

In constructing a three dimensional illuminating object comprising aformed lamp member, the carrier substrate is a biaxially oriented sheetand may be a polyester or a polycarbonate material and the thermoplasticlayers are comprised of polyvinylidene fluoride. Prior to pressureforming the lamp member, the lamp member is heated to a moldingtemperature below the glass transition temperatures of the thermoplasticof the carrier substrate and of the thermoplastic of the superposedlayers and thereafter the lamp member is cooled in the moldedthree-dimensional form. The molding temperature is below a temperatureat which substantial shrinking of the carrier substrate occurs. Themolding temperature is in the range between 190° F. and 270° F. and ispreferably between 230° F. and 260° F.

In general, the achievement of a single overall lamp module that ispractical and inexpensive to manufacture, and which selectively emitsvarious qualities of light at freely selectable locations is aparticularly important practical achievement of the present invention.Another important achievement is the practical achievement ofthree-dimensional electroluminescent lamps and structures carrying suchlamps.

Other advantages and features of the invention will become apparent fromthe following description and from the claims.

DRAWINGS

FIG. 1 is an exploded view of a hand-held remote control unit havingsurface mounted electroluminescent lamps according to the invention.

FIG. 2 is a cross sectional side view taken along lines 2--2 of FIG. 1.

FIGS. 3A-3D are cross sectional side views of a surface mounted lampbeing bonded to a substrate.

FIGS. 4A-4B are top views of surface mounted lamps bonded to asubstrate.

FIG. 5 is a plan view of a surface mounted lamp assembly station.

FIG. 6 is another embodiment having surface mounted lamps according tothe invention.

FIG. 7 is an enlarged view of the flexible circuit of FIG. 6.

FIG. 8A is an exploded view of a sign having surface mounted lampsaccording to the invention.

FIG. 8B is an assembled view of the sign of FIG. 8A.

FIG. 8C is a cross-sectional side view of an electroluminescent lamptaken along lines 8C--8C of FIG. 8B.

FIG. 9 is a cross-sectional view of a surface mounted lamp attached to aflexible substrate using a mechanical eyelet.

FIG. 10 is a cross-sectional view of a surface mounted lamp attached toa flexible substrate using an adhesive strip.

FIG. 11A is a side view of an arrangement for forming anelectroluminescent lamp.

FIG. 11B is a top view of the formed electroluminescent lamp provided bythe arrangement of FIG. 11A.

FIG. 11C is a side view of the formed electroluminescent lamp providedby the arrangement of FIG. 11A.

FIG. 12A is a perspective view of an electroluminescent lamp havingmolded spring detents.

FIG. 12B is a cross-sectional side view of the electroluminescent lamptaken along lines 12B--12B of FIG. 12A.

FIG. 12C is a perspective view of an electroluminescent lamp with moldedspring detents for insertion into a mating receptacle.

FIG. 13A is a side view of a variable light source electroluminescentlamp in its fully extended position.

FIG. 13B is a side view of a variable light source electroluminescentlamp in its fully compressed position.

FIG. 13C is a perspective view of the variable light sourceelectroluminescent lamp of FIGS. 13B and 13C used as an indicator in aspeedometer.

FIG. 14A is an exploded view of a hand-held telephone having a moldedelectroluminescent lamp according to the invention.

FIGS. 14B-14C are cross-sectional side views of the electroluminescentlamp taken along lines 14B--14B and 14C--14C, respectively of FIG. 14A.

FIG. 15A is a plan view of a decorative figure having embossedelectroluminescent lamps.

FIG. 15B is a front view of an embossed electroluminescent lamp of FIG.15A.

FIG. 15C is a side view of an embossed electroluminescent lamp of FIG.15A.

FIG. 15D is a top view of an embossed electroluminescent lamp of FIG.15A.

FIG. 16 is a cross-sectional side view of an alternate arrangement forforming an electroluminescent lamp.

DETAILED DESCRIPTION

Referring to FIG. 1, a hand-held remote control device 10 forcontrolling a number of audio/visual instruments (e.g. television, VCR,stereo receiver) includes a housing 12 having a cavity 14 supporting abattery 16 and a control board 18. Control board 18 includes components20 used to distribute power and signals for generating an infraredcontrol signal to be received by the instruments. In addition, a switchkeypad 22, a modular lamp circuit 24, and a graphics panel 26 aredisposed within cavity 14 in vertical succession. Graphics panel 26includes a graphic having areas 27, 28, 29 associated with eachcontrolled component. Each area 27, 28, 29 further has regions 27a-27n,28a-28n, 29a, 29n designating particular functions (e.g. on/off, volume,channel select) associated with the component designated for that area.A bezel (not shown) may be used to secure the graphics panel 26 tohousing 12. With this arrangement, remote control unit 10 has anilluminated tactile membrane keypad operated by depressing regionsassociated with a selected audio/visual instrument.

Switch keypad 22 includes a flexible polyester board 30a havingconductive traces 32 connected to control board 18 with a switch board30b disposed thereon. Switch board 30b includes shorting switches 34,each switch corresponding to a particular function of a particularcomponent and positioned over a region of circuit board 30a such thatapplication of a downward force on the switch effectively "shorts"traces 32 corresponding to a particular function.

Modular lamp unit 24 produced using techniques of the present inventionis disposed between switch keypad 22 and graphics panel 26 and includesa flexible printed circuit substrate 35 having conductive traces 36 ofconductive ink upon which a number of flexible electroluminescent lamps40 have been placed. Each electroluminescent lamp 40 has a pair ofconductive pads 41a (FIG. 4A) formed by conductive ink deposits on theplastic substrate. These conductive pads provide electrical connectionpoints to conductive traces 36 leading to power and ground buses.Portions of conductive traces 36 that are not connection points toconductive pads 41a of lamps 40, are generally covered with a dielectriclayer to provide electrical isolation, reduce silver migration, and toprovide moisture protection. One method of providing such a dielectriclayer is to screen print a UV curable ink, for example, Product No.5014, manufactured by E.I. DuPont de Nemours & Co., Wilmington, Del.,over portions of conductive traces 36 on flexible substrate 35. Flexiblesubstrate 35 is made from a polyester based material, model no. ST505, aproduct of ICI Corp., Wilmington, Del. having a thickness of about 0.007inches and a surface with a coating of indium tin oxide subsequentlyapplied.

Referring to FIG. 2, an exemplary electroluminescent lamp 40 is shown.It is limited in size to a specific area to be illuminated and comprisesa number of layers beginning with a transparent substrate 42, (e.g., asheet of polyester film approximately 0.007 inches thick). Substrate 42has on one side a pre-applied coating of a transparent conductivematerial, preferably, indium tin oxide (ITO), although aluminum oxide,gold and silver or other composite coatings may also be used. The ITOmaterial is preferably vacuum sputtered onto the substrate panel to forma transparent front coating 44 that is approximately 1000 Å thick.Transparent front coating 44 is covered with a phosphor layer 46 formedof electroluminescent phosphor particles, e.g., zinc sulfide doped withcopper or manganese which are dispersed in a polymeric binder. Phosphorlayer 46 is applied to the front transparent coating 44 by screenprinting and has a thickness of approximately 0.001 inches. A dielectriclayer 48, approximately 0.001 inches thick, is formed of a highdielectric constant material, such as barium titanate dispersed in apolymeric binder. Dielectric layer 48 is screen printed over phosphorlayer 46 so that it extends to the edges of the lamp 40. Deposited overthe dielectric layer 48 is a rear electrode 50 formed of conductiveparticles, e.g., silver, or carbon, dispersed in a polymeric binder toform a screen printable ink. The ink is screen printed onto dielectriclayer 48 to form rear electrode 50 in a layer approximately 0.0005inches thick. In some applications of lamp 40, an additional insulatinglayer (not shown) may be applied over rear electrode 50 to preventpossible shock hazard or to provide a moisture barrier to protect thelamp. A suitable polymeric binder for these layers is PVDF as describedin U.S. Pat. No. 4,816,717, incorporated herein by reference.

Referring again to FIG. 1, each of the pre-formed electroluminescentlamps 40 is positioned between particular shorting switches 34 of switchkeypad 22 and corresponding areas 27, 28, 29 of graphics panel 26. Theflexible nature of lamps 40 permits the downward force applied to coverplate 26 to be transferred to shorting switches 34 without damaginglamps 40. In this embodiment, electroluminescent lamps 40 associatedwith particular regions of graphics panel 26 have different selectedcolors. For example, area 27 associated with television functions isilluminated with an electroluminescent lamp 40a emitting orange lightwhile area 29 associated with controlling a video cassette recorder(VCR) is illuminated with lamp 40b emitting blue light.

Referring to FIGS. 3A-3D, a process for bonding the small pre-formedelectroluminescent lamps 40 to the flexible substrate 35 of the modularunit is shown.

As shown in FIG. 3A, lamp 40 with lit side 33 facing up is positioned onflexible substrate 35 such that conductive pads 41a, 41b of the lamp aresuperposed over traces 36 of the substrate. A small drop of adhesive oras shown here, a double-sided pressure sensitive adhesive strip 52 isplaced between flexible substrate 35 and rear electrode 50 of lamp 40 ata region between conductive pads 41a, 41b to lightly fasten lamp 40 toflexible substrate 35. Referring back to FIG. 2, conductive pad 41b isdirectly connected to rear electrode 50 while conductive pad 41a isconnected to transparent front coating 44 through a via hole (notshown). Adhesive strip 52 permits the lamp 40 and flexible substrate 35combination to be flipped over during the course of manufacture suchthat lamps 40 are beneath the board for reasons as explained below.

Referring to FIG. 3B, lamp 40 is electrically and mechanically bonded toflexible substrate 35 using an ultrasonic welder 54 (FIG. 5), such asModel 901AE IW Integrated Welder, manufactured by Branson UltrasonicsCorp., Danbury, Conn. As described above in conjunction with FIG. 3A,the lamp 40 and flexible substrate 35 combination may be flipped overand provided to welder 54 so that an under surface 37 of flexiblesubstrate 35 faces a knurled welding tool 56 positioned above the regionof conductive pad 41a of lamp 40. Knurled welding tool 56 has a diameterof about 0.25 inches and a tip having a grid array of relatively sharpprongs 60 approximately 0.020 inches long and spaced from each other by0.030 inches. With this arrangement, transparent coating 44 of lamp 40is face down on an X-Y base plate 58 of welder 54. Welder 54 iselectronically programmed to position welding tip 56 over a planeparallel with base plate 58.

As shown in FIG. 3C, welder 54 is programmed to lower knurled weldingtool 56 to undersurface 37 with a predetermined force and for a preciseduration of time so that prongs 60 penetrate through flexible substrate35 and into lamp 40. Prongs 60 extend through rear electrode 50,phosphor 46 and into transparent substrate 42 of lamp 40. As is known bythose in the art, vibration welding is a technique for producing strongstructural or high-pressure seals between thermoplastic materials. Highfrequency electrical energy (20 kilohertz) is provided by a solid statepower supply to a converter unit (not shown) of welder 54. The converterunit changes the electrical energy into mechanical vibratory energy atultrasonic frequencies. The vibratory energy is transmitted to the jointarea through welding tool 56 and is converted to heat at the prongs ofthe tool through friction. In this embodiment, the undersurface 37 offlexible substrate 35 is vibrated against the rear electrode 50 of lamp40 under a pressure of 10-20 lbs/in², for 25-75 milliseconds. Frictionalheat generated at the interface area causes the polyester material offlexible substrate 35 and transparent substrate 42 to fuse such that astrong molecular bond is provided therebetween.

Referring to FIG. 3D, to complete the weld operation, knurled weldingtool 56 is lifted away from flexible substrate 35 leaving behindmechanical contact points 62 of fused polyester of flexible substrate 35and transparent substrate 42 of lamp 40. The weld strength of mechanicalcontact points 62 approaches that of the parent material. Concurrently,the localized heat and vibration provided by the knurled welding tool 56forces the screen printable conductive polymeric ink of rear electrode50 away from the penetration locations to form electrical contact paths64 between mechanical contact points 62, so that electrical continuityis assured.

Referring to FIGS. 4A and 4B, lamp 40 is shown having a pair ofconductive pads 41a attached to conductive traces 36 of flexible circuit35. The grid arrangement of prongs 60 of welding tool 56 is used toprovide the grid of fused mechanical contact points 62 and conductiveink to conductive ink electrical contact paths 64 between printed rearelectrode 40 and printed conductive traces 36. A line of interruption 69is laser scribed through rear electrode 50 to provide electricalisolation between the rear electrode 50 and front electrode 44.Electrical isolation is provided because connection of rear electrode 50to flexible substrate 35 as described in FIGS. 3A-3D (or when usingmethods described below) can cause front electrode 44 to short with rearelectrode 50.

It is appreciated that the small, pre-formed lamps 40 may be connectedto flexible substrate 35 using other attachment means. Referring to FIG.9, for example, a mechanical eyelet 120 is shown having a headed pinportion 122 that is disposed through lamp 40 and flexible substrate 35and flattened at a bottom surface 39 of substrate 35 to fasten lamp 40firmly to the substrate. Alternatively, as shown in FIG. 10, a strip ofstrong conductive adhesive film 130, such as Model No. 9703, a productof 3M Corporation, Minneapolis, Minn. is used to securely fix lamp 40and substrate 35.

The process of securing preformed lamps 40 of selected small size toflexible substrate 35 is advantageously adapted for use in an automatedproduction line environment. Referring to FIG. 5, an automated lampmounting assembly line 70 is supplied an inventory of flexiblesubstrates 35 having predetermined conductive traces 36 andpredetermined areas for securing lamps 40. Flexible substrates 35 areconveyed along a line past a series of production stations. At apreparation station 72, for example, substrates 35 are cleaned andprepared for receiving lamps 40 before being conveyed to loading station73. Each substrate 35 is generally supported on a rigid template toprovide support to the flexible substrate as it moves from station tostation and to provide registration for the welding procedure. Assemblyaides such as adhesive tape 52, 130 (described in conjunction with FIGS.3A and 10) or epoxy adhesives are placed at appropriate locations onflexible substrate 35 at an adhesive dispensing station 74. Dispensingstation 74 here, includes a syringe that is controlled to dispense a"dot" of quick-drying epoxy, sufficient for supporting a lamp 40, ontoan area of the lamp removed from conductive pads 41a.

Lamps 40 are placed on substrates 35 in a "pick and place" fashion at anumerically controlled lamp-mounting station 75 having a robot arm 76. Awide variety of lamps 40 having different sizes, colors, and intensitiesare supplied from selection trays or from a spool of flexibleelectroluminescent lamps. A bill of instructions defining the number,type, and position of lamps 40 to be bonded to flexible substrate 35 isprovided to assembly line 70 to instruct robot arm 76 to select andproperly position lamps 40 on flexible substrate 35. The robot arm 76uses a vacuum pick up mechanism to retrieve lamp 40 having uncured epoxyapplied thereto, positions, and presses the lamp for a sufficient timeto allow the epoxy to partially cure and returns to retrieve a nextlamp.

For certain modular lamp assemblies, it may be necessary to use a flipstation 77 to turn the flexible substrate/lamp combination over so thatunderside 37 (rear electrode 50) is presented face up to a series ofwelding stations 78a-78c. In such applications, the template is used toflip over flexible circuit 35.

Each one of welding stations 78a-78c operate as described above inconjunction with FIGS. 3B-3D to mechanically and electrically secure aparticular lamp 40 to the flexible substrates 35 at a preselectedposition. In an alternate arrangement, a single welding station having anumerically controlled robot arm may be used to perform weldingoperations for all of the lamps 40 positioned on substrate 35.

Finally, completed modular lamp units are conveyed to an unload station79 where they may be cleaned, inspected, tested and packaged fordelivery.

Other embodiments are within the scope of the claims. For example,referring to FIG. 6, the interior of an automobile is shown to includean automobile dashboard 80 having an instrumentation mount 82 forsupporting a dash panel 88 and gauges 84-87. Instrumentation mount 82has a concave shape conforming with the curved dashboard of the stylizedautomobile cockpit. Gauges 84-87 include, for example, speedometer,tachometer, temperature, and fuel gauge functions. Dash panel 88includes a printed graphic for warning indications 89-94, such as seatbelt, open door/trunk, high beam headlight and alternator functions.

Referring to FIG. 7, a pre-formed, flexible multi-lamp module unitmanufactured in the manner described above is positioned withininstrumentation mount 82 and behind both gauges 84-87 and dash panel 88.Flexible circuit 95 of the module is shown carrying electroluminescentlamps 84a-87a and 89a-94a connected with conductive traces 96 of thesubstrate to an electrical power source (not shown). Electroluminescentlamps 84a-87a and 89a-94a have sizes and shapes conforming withcorresponding gauges 84-87 and warning indications 89-94 to beilluminated. Each electroluminescent lamp 84a-87a and 89a-94a isindependently addressable and where appropriate is connected to a switchfor connecting the lamp to the power source when a particular fault(e.g., seat belt unfastened) is detected. The multi-lamp flexible modulemay be deformed or flexed to the extent that regions having small radiiof curvature exist. In these regions, flexible circuit 95 and attachedlamps 84a, 87a may include strain relief incisions 97 to reduce bendingstress 40 on lamps 84a, 87a and flexible circuit 95.

In another embodiment, not shown, the multi-lamp flexible module unitshown in FIG. 7 may be formed by employing, as a carrier substrate, arelatively thick self-supporting substrate of thermoplastic which, aftermanufacture in the flat, is formed by application of pressure and heatwith lamps in place into a desired configuration.

In the case of forming the lamps themselves into three-dimensionalobjects, it is found advantageous to employ a process we refer to as"thermalforming". Thermalforming is distinguishable from the well-knownprocess of thermoforming in which a plastic film is heated to its glasstransition temperature and allowed to sag, before drawing it over orinto a die by vacuum and/or pressure. Thermalforming is a very differentprocess that is conducted at lower, controlled temperatures below theglass transition temperature, in which pressure forming action isemployed to conform the lamp to a mold without disturbing theoperational integrity of the layers of the lamps. Thus, the lamp, in itsnew three-dimensional form, can still function as a lamp. For example,certain types of electroluminescent lamps such as the Durel-3™electroluminescent lamp, manufactured by Durel Corporation, Tempe,Ariz., are fabricated on a carrier substrate comprising a biaxiallyoriented polyester film which is found to be conducive for beingthermalformed into a wide variety of three dimensional configurations.Alternatively, such electroluminescent lamps may be provided onpolycarbonate films. Generally, the temperature limits forthermalforming lamps provided on such substrates is between 190° F. and270° F., with a preferred range between 230° F. and 260° F. The upperlimit is limited by the temperature at which the thermoplastic layers ofthe electroluminescent lamp are damaged and further, in the case oforiented polymeric substrates, by the temperature at which the carriersubstrate is subject to shrinking. The thermoplastic layers of the lampare generally comprised of polyvinylidene fluoride and include a layercontaining phosphor particles for forming a phosphor layer, aninsulative layer and a layer, e.g., containing conductive particles, forforming a back conductive electrode. It is important to note that therange of temperatures suitable for thermalforming is well below theglass transition temperatures of polyester and polycarbonate. The lowertemperature limit is established by the temperature required topermanently deform the lamp. Thermalforming at these relatively lowtemperatures maintains the integrity of the carrier substrate andthermoplastic layers. Specifically, the phosphor layer, afterthermalforming, provides a uniform distribution of light across the lampand reliable electrical continuity is maintained across the conductivelayer. In addition, shrinkage of the carrier substrate is avoided duringthe thermalform process.

Referring to FIG. 11A, one method of thermalforming anelectroluminescent lamp includes the heating of mated, male and femalealuminum dies 140, 142 in an oven (not shown) to 250° F. A Durel-3 ELlamp 144 is placed between the dies 140, 142 and a "C" clamp 146 is usedto provide slight pressure to hold the sandwiched parts together. Thesandwiched lamp 144 and clamp 146 is returned to the oven at the sametemperature for approximately eight minutes, is removed and the clamp146 tightened. After 15 minutes of cooling, the clamp 146 is removed toprovide the thermalformed lamp 144a. The thermalformed lamp 144 whenattached to a power supply, illuminates with uniform lighting providedin both thermalformed and flat regions of the lamp. As shown in FIGS.11B and 11C, the shape of aluminum dies 140, 142 provide lamp 144a witha circular groove 148 and was used to demonstrate the degree of thermaldeformation that the lamp 144 can experience during thermalformingwithout impairing its function.

In another application, shown in FIGS. 12A-12B, the planar pad portions150 of a Durel 3 electroluminescent lamp 151 for supporting electricalcontacts 152 are thermalformed in the manner described above inconjunction with FIGS. 11A-11C to provide spring detents. The padportions are preferably deformed to be elevated above the plane of thesurface of the electrode about 0.010 inch, although in certainapplications 0.002 inches may be sufficient to provide the necessaryspring effect. In applications where electrical power is provided tocontacts on opposite surfaces of an electroluminescent lamp, conductiveadhesives are typically used to maintain good electrical contact at thecontact points. The spring detents provide constant pressure to theconductive adhesive at the connection point assuring electricalcontinuity to the lamp and its power source.

In another embodiment, as shown in FIG. 12C, an electroluminescent lamp154 has integral raised polymeric spring detents 153 thermalformed oncontact pads for insertion into a receptacle 155. Receptacle 155includes a mating connector having spring fingers 157 with a dimensionslightly less than the height of detents 153. The spring detents 153formed of the polymer of the lamp itself are compressed during insertionsuch that a wiping action is imparted between the contacts. It isappreciated that although FIGS. 12A-12B show the detents on oppositesides of the lamp, constructions with the detents on the same surface ofthe lamp are also possible.

In another embodiment, a thermalformed lamp may be constructed toprovide a variable light output lamp 156. Referring to FIGS. 13A-13B, aone inch wide, eight inch strip 158 of Durel-3 EL lamp material isformed into a helical spiral of coils 160, adhesively clamped around acylindrical mandrel and placed in a 250° F. thermal oven for 5 minutes.The clamped lamp material 158 is removed from the mandrel and allowed tocool for 7 minutes. Upon removal, the EL lamp 156 remains as a helicalspring that can be compressed, but is biased to return to its elongatedform. Referring to FIG. 13B, the EL lamp 156 when telescoped to itsfully extended form, emits the maximum amount of light from the helicalcoils 160. Conversely, as shown in FIG. 13A, to reduce the lightemitted, the helical coils 160 are compressed such that masking betweenthe individual coils reduces the overall light emitted from the lamp156. As shown in FIG. 13C, the variable light output lamp may be usedfor example in a automobile speedometer. In this embodiment, thevariable light output lamp is mounted within the dash panel and isattached to the automobile's speedometer cable to provide the pressurenecessary to permit the illuminated coils to elongate as the speed ofthe automobile is increased and shorten when the speed is decreased.

Referring to FIG. 14, in another embodiment, a thermalformedelectroluminescent lamp 170 is shown for providing lighting to the frontgraphic 172 of a hand-held cellular telephone 174. The telephoneincludes a backlit keyboard 176 on two levels and a single thermalformedlamp 170 creased to conform with the transition region of the graphic.Thermal deformation of this degree may, in certain applications, causecracking of the indium tin oxide (ITO) conductive coating and the rearelectrode carbon ink coating of the lamp 170 along conductive traces 178which extend from lamp contacts 180. Damage to the ITO layer of theconductive traces 178 can result in diminished light output from thoseareas of the lamp following the crease. Accordingly, in a preferredembodiment, silver carrier pads 182, in the form of a silver ink areused to bridge across the creased portions in order to maintain areliable electrical connection across the surface of the lamp 170.Referring to FIGS. 14B and 14C, cross-sectional views through thecreased portions of the front and rear electrodes, respectively, of thethermalformed electroluminescent lamp are shown. As is shown in FIG.14B, a polyester carrier substrate 181 with an ITO layer 183 disposedthereon has silver carrier pad 182 screen printed over the portions tobe thermalformed. Phosphor, dielectric and rear electrode layers 184,185 and 186 respectively, are subsequently deposited in succession overthe silver carrier pad and ITO layer. Referring to FIG. 14C, the sameprocess is used to provide a silver carrier pad through a rear electrodeportion of the thermalformed lamp with the exception that the ITO layer183 is laser etched at a region 187 prior to deposition of the phosphor,dielectric and rear electrode layers to provide isolation between thefront and rear electrodes.

Because the mechanical force necessary to deform a structuralthermoplastic circuit board member is generally greater than thatrequired to deform the relatively thin polyester based flexibleelectroluminescent lamp, it may be desirable, in some applications, tothermalform the lamp prior to placing it on the three-dimensional shapedreceptor surface portion of its mating printed circuit. Thus, the lampis thermalformed to provide a three-dimensional shaped lamp membercooperatively sized and shaped to match with the three-dimensionalshaped portion of the mating circuit without subjecting the lamp to themechanical stresses that are necessary to form the three-dimensionalstructural portion.

The method of thermalforming can be used to provide three dimensionalityto illuminated objects to highlight particular features and to increasethe aesthetic nature of a product. Emblems or badges used as decorativeor promotional items having illuminated portions may benefit from such amethod. Referring to FIG. 15A, for example, a Christmas tree 190includes electroluminescent lamps 192 representing ornamental ballsplaced on the tree. Each lamp may be thermalformed using a process suchas the approach described above in conjunction with FIGS. 11A-11C tocause the ornamental balls to be raised from the surface of the sheet insemi-spherical form. FIGS. 15B, 15C, and 15D show a thermalformed lampin front, side and top views, respectively. The lamps, embossed in thisway, are more pronounced and more closely represent real Christmasornaments hanging from a tree. In another embodiment, a pair ofsemi-spherical electroluminescent lamps disposed adjacent to each otheron a relatively thin substrate may be hinged together by a living hingeformed by the substrate so that folding one lamp over the other providesa single illuminated spherically shaped lamp.

It is appreciated that thermalforming of electroluminescent lamps may beapplied to provide a raised or embossed image, such as the ornamentalballs described above, or may be "debossed" to provide the image in adepressed form. Both approaches provide the added dimensionality toaccentuate the images represented by the lamps and increase theaesthetics of the normally flat lamp.

Embossing or debossing the electroluminescent lamps may be accomplishedusing the method described above in conjunction with FIG. 11A.Alternatively, an alternative mechanism, as shown in FIG. 16, includes amolding tool member 202 having concave portions 203 representing theshape of the emboss or debossed image. A sheet-form electroluminescentlamp 204 is placed over molding tool 202 and a pneumatic pressure member206 having an elastomeric membrane 208 attached to a rigid backplate 210is used to thermalform lamp 240. In operation, molding tool member 202is heated to the desired temperature and pneumatic pressure member 206lowered until edge portions of rigid backplate 210 engage the surface ofthe lamp. In some embodiments it may be desirable to apply additionalheat through rigid backplate 210. Pneumatic pressure is applied to aninflation port 211 to expand elastomeric membrane 208 with sufficientforce to deform lamp 204 within the concave portions of molding toolmember 202. Heat is removed from molding tool member 202 and after asufficient cooling period, the pneumatic pressure member is deflated andthe thermalformed lamp removed from molding tool member 202.

It is recognized that in applications where the forming of anelectroluminescent lamp does not require precisely defined edges, thelamp may be pressure formed under cooler pressure molding conditions.This, too, will maintain the operational integrity of the carriersubstrate and the thermoplastic layers of the formed lamp. Theembodiments described above in conjunction with FIGS. 11B, 12A, and 14Care examples of applications where pressure forming may be used toproduce a formed shape capable of emitting light. On the other hand, forthose embodiments requiring higher definition and more complex shapes(e.g., embossed alphanumeric symbols) thermalforming within thetemperatures ranges described is preferable. The "C" clamp and pneumaticpressure producing arrangements described above in conjunction withFIGS. 11A and 16, respectively are both appropriate for pressure formingelectroluminescent lamps.

Referring to FIGS. 8A-8C, electroluminescent lamps 100 are used to lighta sign 99. A polycarbonate substrate 102 having a thickness of about0.020 inches includes a graphic 104 on a front surface 106 withpartially transparent areas 103 representing stenciled letters, forexample, the word "EXIT". On an opposite rear surface 108 of substrate102 conductive traces 110 for conveying power to lamps 100 are providedalong the outer periphery of substrate 102 having connection pads 112for attaching lamps 100. Lamps 100 are here fabricated using the processdescribed above in conjunction with FIG. 2. However, described above inconjunction with FIG. 2. However, because lamps 100 in sign 99 are notrequired to be flexible, rigid lamps may alternatively be employed,still using surface mount techniques, such as described above. Unlikethe embodiments described above in conjunction with FIGS. 1 and 8, litsides 113 of lamps 100 are placed face to face with rear surface 108(ink side) of substrate 102 and held upon substrate 102 using a thinsheet of transparent adhesive 115 (FIG. 8C) so that the emitted lightpasses through transparent regions 103. Referring to FIGS. 8B and 8C,flexible polyester jumpers 114 having silver traces 116 on one surfaceare used to connect rear electrodes on unlit sides 118 of lamps 100 toconnection pads 112 of substrate 102. Connection between lamps 100 andconductive traces 110 may be accomplished using any of the abovedescribed attachment methods described above in conjunction with FIGS.3A-3E, 9, and 10.

What is claimed is:
 1. An electroluminescent lamp assembly comprising:asubstrate having a relatively large lamp receiving surface, having anarray of conductive traces disposed on said surface of said substrate,and a plurality of relatively smaller lamps distributed in spaced-apartrelationship according to a preselected illumination pattern over, andsecured to, said lamp receiving surface, at least one of said lampscomprising: a mechanically flexible multi-layer sheet-formelectroluminescent lamp including a sheet-form layer containingelectroluminescent particles, said layer disposed between a pair ofsheet-form conductive layers, at least one of which is transparent fortransmitting light emitted from said particles, and at least one ofwhich is mechanically flexible, said electroluminescent lamp havingconductors exposed for engagement with said conductive traces on saidsubstrate, said electroluminescent lamp being surface mountedface-to-face to said substrate in the manner that its conductors engageselected conductive traces on said lamp receiving surface.
 2. Theelectroluminescent lamp assembly of claim 1 wherein said multi-layersheet-form electroluminescent lamp has a first light emittingcharacteristic different than a second light emitting characteristic ofanother of said plurality of relatively smaller lamps.
 3. Theelectroluminescent lamp assembly of claim 2 wherein said first lightemitting characteristic has a different color from that of said secondlight emitting characteristic.
 4. The electroluminescent lamp assemblyof claim 2 wherein said first light emitting characteristic has adifferent intensity from that of said second light emittingcharacteristic.
 5. The electroluminescent lamp assembly of claim 1wherein said substrate is a flexible substrate.
 6. Theelectroluminescent lamp assembly of claim 1 wherein said substrate hasan initial shape and is deformed with said surface mountedelectroluminescent lamp into a deformed shape.
 7. The electroluminescentlamp assembly of claim 6 wherein said substrate is mechanicallydeformable.
 8. The electroluminescent lamp assembly of claim 6 whereinsaid substrate is a flexible substrate.
 9. The electroluminescent lampassembly of claim 6 wherein said substrate includes a strain reliefincision and a desired final configuration of complex shape.
 10. Theelectroluminescent lamp assembly of claim 1 wherein said plurality ofrelatively smaller lamps further comprises a rigid lamp.
 11. Theelectroluminescent lamp assembly of claim 10 wherein said rigid lamp isof smaller area than said multi-layer sheet-form electroluminescentlamp.
 12. The electroluminescent lamp assembly of claim 10 wherein saidrigid lamp is surface mounted face-to-face to said substrate.
 13. Theelectroluminescent lamp assembly of claim 1 further comprising securingmeans for attaching the multi-layer sheet-form electroluminescent lampto said lamp receiving surface of said substrate.
 14. Theelectroluminescent lamp assembly of claim 13 wherein said securing meanscomprises a thermal bond between a substance of said lamp and asubstance of said substrate.
 15. The electroluminescent lamp assembly ofclaim 14 wherein said thermal bond comprises an ultrasonic weld.
 16. Theelectroluminescent lamp assembly of claim 13 wherein said securing meanscomprises a mechanical fastener.
 17. The electroluminescent lampassembly of claim 13 wherein said securing means comprises a localizeddeposit of adhesive at a region of engagement between said conductors ofsaid electroluminescent lamp and said selected conductive traces on saidlamp receiving surface of said substrate.
 18. The electroluminescentlamp assembly of claim 13 wherein said securing means only contacts theflexible multi-layer sheet-form electroluminescent lamp at the same lampsurface that the substrate's conductors contact the lamp surface.